1. Field of the Invention
This invention relates to a pressurized port for viewing the interior of a molten metal bath contained in a treatment vessel and, with use of an optical sensor, for measuring the temperature, composition, or other properties of the molten metal bath.
2. Description of the Prior Art
In the production and/or treatment of metals in a molten metal bath, it is necessary to determine the temperature, composition or other properties of the molten metal bath. Such processes do not allow direct inspection because the molten metal is contained in a refractory lined furnace and, in such production processes, a layer of slag floats on top of the metal during processing. In order to determine the temperature and chemical composition of the metal, devices are inserted through the slag into the metal. The high temperatures involved do not permit the use of materials other than refractories to come in contact with the molten metal for any extended period of time.
In the past, the method for determining temperature of such molten metal baths has required inserting an expendable thermocouple into the bath, in which case the thermocouple is used for only one test, then discarded or destroyed. The method of analyzing the chemical composition of the bath is to withdraw a sample of the metal and send it to a laboratory for analysis. Insertion of such devices, and the withdrawing of samples, requires that the production process be stopped, thus delaying the process. Further time delays occur while the samples are transported and analyzed. Since direct inspection cannot be done, predictive calculations must be made to determine the amount of reactive materials required to reach the desired temperature and composition.
Various attempts have been made to avoid such indirect methods of analyzing molten metal baths.
For example, U.S. Pat. No. 4,106,756 discloses an oxygen lance and sensor system consisting of an optical sensor mounted on an oxygen lance suspended above the molten metal bath for monitoring the furnace and bath. The view thus provided is of the upper surface of the bath consisting of a highly agitated and heated mixture of metal and slag due to oxygen blowing onto the surface of the bath.
U.S. Pat. No. 4,377,347 relates to use of a probe, comprising a thermocouple covered with ceramic fiber, inserted through a vessel wall and immersed in the molten metal bath, and generating a signal proportional to bath temperature which is sent to an external pyrometer; it typically is used in a continuous caster tundish. There is no direct viewing of the bath.
U.S. Pat. No. 4,416,443 discloses a thermocouple attached to a concentric pipe tuyere extending through the bottom of a furnace wherein the thermocouple is used to warn of high tuyere temperatures indicating tuyere blockage.
U.S. Pat. No. 4,651,976 shows a furnace having a side opening, above the surface of the metal bath in the furnace, in which opening there is disposed an optical device, such as a photometer, to view the light level above the bath for determining the amount of slag being formed. There is no direct viewing of the bath.
U.S. Pat. No. 4,842,253 relates to an optical device mounted in a port in the side of a blast furnace or the like and with its field of view arranged to include the combustion zone of an adjacent tuyere in order to monitor combustion conditions in the furnace.
U.S. Pat. No. 5,071,105 discloses a gas torch having an optical lens and fiber assembly fitted into the torch to provide visual observation of the high temperature process resulting from operation of the torch.
U.S. Pat. No. 5,397,108 discloses a peepsight for a blast furnace tuyere system, in which a fiber optic cable is disposed opposite a viewing port of a sleeve extending into the furnace wall and carries a light signal to a photosensitive sensor.
Industry Net publication of September 1996 discloses an oxygen lance for a top-blown oxygen furnace, in which a pyrometer is mounted inside the lance to measure the temperature of the hot spot of metal and slag where the oxygen jet impinges on the surface of the bath.
A recent paper entitled "Direct Analysis in Steelmaking Converters Using Laser-Induced Emission Spectrometry," C. Carlhoff and S. Kirchhoff, Krupp Forschungsinstitut, Essen, Germany, discloses the use of a laser beam directed, through an opening in the side of the furnace, onto the bath surface, producing a hot plasma, and the generated light is carried by a fiber optic cable to a spectrometer.